Seeking the Right Dev-QA Ratio on an Agile Team

There has been a long-standing debate on what is the right ratio of developers to QA (dev-QA) on software engineering teams. Many managers face this debate on a regular basis. Some people argue that you need to keep a 1-to-1 ratio of dev-QA, whereas others say that you need no QA people on The Team and that developers should be responsible for the code they write.